DESCRIPTION (Verbatim from Applicant's Abstract): Abdominal aortic aneurysm (AAA) is a focal enlargement of the infrarenal aorta. If left untreated, AAA will gradually expand until rupture; an event that carries a mortality rate of 90 percent and which is ranked as the 13th most common cause of death in the US. Associated with surgical repair of AAA are significant costs and risks to the patient. Thus, it is important to determine when the risk of rupture justifies the risks associated with surgery. The ability to reliably evaluate the susceptibility of a particular AAA to rupture could vastly improve the clinical management of these patients, as there presently exists no such reliable evaluation criterion. AAA rupture occurs when the mechanical stress (i.e., internal forces) acting on the aneurysm wall exceeds its ability to withstand these stresses (i.e., the wall's failure strength). The greater the wall stress to wall strength ratio for a particular AAA, the greater the likelihood of rupture. They therefore believe that a "biomechanics-based approach" would lead to an improved assessment of the propensity for rupture of AAA on a patient-specific basis. Before the decision is made for surgical intervention for an individual patient, the investigators believe that the surgeon should know two things: the mechanical stress acting on that aneurysm and the strength of the AAA wall. They have recently made great strides toward these ends. However, to improve their AAA wall stress estimates the biomechanical behavior of the AAA wall needs to be more carefully and rigorously defined. Therefore, Specific Aim #1 is to refine their current methodology to account for the more realistic, anisotropic biomechanical behavior of AAA. They previously showed that there occurs a significant, 50 percent decrease in strength of the AAA wall versus nonaneurysmal aorta. However, they did not determine spatial variation of AAA wall strength. Specific Aim #2 is to develop a statistically based, multifactorial model to noninvasively estimate spatial variation of AAA wall strength. Specific Aim #3 is to generate the spatial variation of the rupture potential index (RPI) for individual AAA. The RPI is defined as the locally acting wall stress divided by the local wall strength. As the RPI nears a value of 1.0, AAA rupture is imminent. The clinician may therefore inspect the RPI distribution in order to make an evaluation for a particular AAA. This novel, innovative, computer-based noninvasive method would be an important and reliable diagnostic tool to guide the surgeon in decisions for elective repair of AAA, greatly improving the clinical management for those afflicted with this disease.